1. Field of the Invention
The present invention relates to a process and a device for bonding two millimeter elements. Millimeter elements operate at frequencies typically greater than 30 Ghz. In particular, the invention enables bonding two millimeter elements having microstrip conducting lines.
2. Discussion of the Background
Printed circuits, on which millimeter circuits are made, can have at least two types of propagation lines.
A first type is said to be coplanar because the printed circuit implements coplanar lines. A coplanar line consists of a conducting line surrounded by two ground planes situated symmetrically on either side of the conducting line, the conducting line and the ground planes being situated on the same face of the substrate of the printed circuit. The bonds between millimeter circuits are formed by wires. These bonds can introduce disturbances when the circuits to be bonded are too far apart. This is because an electric field spreads horizontally between the central conductor, connected to the conducting line, and the lateral conductors, situated on either side, connected to the ground planes. The characteristic impedance of this propagation line is determined mainly by the ratio between the width of the conductor and the width of the space between the central conductor and the lateral conductors, as well as by the dielectric constant of the support, namely air.
The second type is the so-called microstrip because the printed circuit implements microstrip lines. The printed circuit thus comprises a dielectric substrate with two main faces, an upper face and a lower face. A conductor having the shape of a strip is formed on the upper face and a ground conductor is made on the entirety of the lower face. In accordance with this arrangement an electric field spreads between the strip-like conductor and the ground conductor. When manufacturing a microwave-frequency device, various millimeter elements are arranged in a metal casing. The millimeter elements may consist of millimeter circuits formed on a printed circuit, of substrates or of components. Each millimeter element is attached to a bedplate screwed onto the metal casing. Under these conditions, ground continuity is achieved on the one hand by soldering or by conductive cementing to the entire surface of the printed circuit and on the other hand by screwing the bedplate to the metal package. In the millimeter frequency region, the ground continuity of the microwave-frequency device described above may not be of sufficient quality. In particular, when ground continuity is ensured by contact, between a package screwed onto the casing and the casing, for example, the latter may not be of good quality, if the screwing is insufficient or if the surfaces in contact are not perfectly plane. Moreover, when two millimeter circuits to be bonded are far apart, the techniques described above may not be useable.
An object of the invention is to alleviate the above drawbacks.
One embodiment of the device of the present invention is a millimeter element including:
a substrate having an upper face and a lower face;
a conducting line on the upper face and oriented substantially perpendicular to an edge of the substrate; and
two continuous bounding zones on the upper face and along the edge of the substrate, each continuous bounding zone being electrically grounded, and having a length between about two and about five times the width of the conducting lines.
One embodiment of the method of present invention includes:
forming a first conducting line on an upper face of a first substrate and perpendicular to an edge of the first substrate;
forming a second conducting line on all upper face of a second substrate and perpendicular to an edge of the second substrate;
forming two continuous bounding zones on the upper face of the first millimeter element and along the edge of the first substrate, each continuous bounding zone being electrically grounded, and having a length between about two and about five times the width of the conducting lines;
forming two continuous bounding zones on the upper face of the second millimeter element and along the edge of the second substrate, each continuous bounding zone being electrically grounded, and having a length between about two and about five times the width of the conducting line;
connecting the conducting line of the first millimeter element to the conducting line of: the second millimeter element; and
connecting the continuous bounding zones of the first millimeter element to the continuous bounding zones of the second millimeter element.